Vacuum energy has been measured since the early 20th century, but its existence remains controversial.
Why? Because vacuum energy isn’t directly observable. How does it work? What is it? And why should anyone care?
What Is Vacuum Energy?
The concept of vacuum energy was introduced by Albert Einstein in 1917. He suggested that empty space contains a kind of energy that is associated with zero pressure. This idea became known as the cosmological constant.
In 1929, Edwin Hubble discovered that galaxies are moving away from each other at ever-increasing speeds. This implied that the universe was expanding.
If the universe is expanding, then the amount of matter and energy in the universe must also be decreasing.
Therefore, the total mass and energy of the universe must be decreasing over time. This means that the total energy of the universe must include some form of negative energy.
This negative energy is called vacuum energy. According to quantum field theory, vacuum energy exists because virtual particles pop into existence out of nothingness.
These virtual particles are constantly popping into existence and disappearing. They are responsible for creating the force of gravity.
Since these virtual particles are popping into existence and disappearing, they are continually changing their energy levels.
As a result, the energy level of the vacuum changes continuously. This change in energy creates a repulsive force that pushes objects apart. The more virtual particles there are, the stronger this force becomes.
Vacuum energy can be thought of as an invisible background energy that permeates all of space. It is not visible because it doesn’t interact with anything.
However, if you could somehow measure the entire energy of the universe, you would find that it includes a large amount of vacuum energy.
How Can Vacuum Energy Be Measured?
Because we cannot actually see vacuum energy, that makes it tricky to measure. But not impossible. We can use indirect methods to determine whether or not vacuum energy exists.
For example, scientists have observed that the expansion rate of the universe appears to be accelerating.
Accelerating expansion implies that something is pushing outward on everything else. That something is probably vacuum energy.
Another method involves measuring how much dark energy is present in the universe. Dark energy is another name for vacuum energy.
Scientists know that dark energy is causing the acceleration of the universe’s expansion.
So far, they haven’t found any evidence of dark energy itself. To detect dark energy, scientists need to look for the effects that dark energy causes.
One way to do this is to study the motion of distant supernovae.
Supernovae occur when massive stars die. When a star dies, its core collapses under its own weight. This collapse releases tremendous amounts of energy. Some of that energy escapes the dying star as light.
The rest goes inward toward the center of the star. This process continues until the star has collapsed down to a white dwarf.
At this point, the star is so dense that electrons and protons fuse to create neutrons. The neutrons become part of the white dwarf.
When a supernova occurs, the explosion sends shock waves through the surrounding area. These shock waves cause nearby gas clouds to expand rapidly.
This expansion produces a bright flash of light. By studying the brightness of these flashes, scientists can measure the distribution of dark energy throughout the universe.
The most direct measurement of vacuum energy comes from cosmological observations. Cosmologists observe the universe at different times by looking at galaxies billions of light-years away.
They then compare the distances between those galaxies to calculate how fast the universe expands over time.
If the expansion of the universe were slowing down instead of speeding up, that would mean that something was pulling things apart.
In other words, something would be pushing against the universe’s fabric. That something would have to be vacuum energy.
Vacuum Energy Explained
To understand why vacuum energy is important, it helps to first consider what happens when you boil water. As soon as the temperature reaches 100 degrees Celsius (212 degrees Fahrenheit), the water starts boiling.
The water molecules start bouncing around more quickly than usual. The water becomes less dense. And the pressure inside the container rises.
This is similar to what happens when you heat empty space. Space gets hotter and hotter as you go farther out into space.
Eventually, there isn’t enough room for all of the particles that make up space to move around freely. Instead, some of them get stuck together.
This means that space is no longer completely empty. There are still lots of particles floating around, but they aren’t moving very quickly.
As long as we live on Earth, we will never see space get hot enough to boil off all of the particles that compose it.
But if we travel to outer space, we might find ourselves in an environment where space is getting hot enough to boil off some of the particles. We could even find ourselves in a place where space is boiling off all of the particles!
This situation is called the “vacuum state.” It represents a special kind of state of matter. A vacuum state exists when there is nothing left in the container except for the empty space.
You can think about a vacuum state like a giant pot of boiling water. Once the water boils, there is no liquid water—just empty space.
There is one big difference between a normal state of matter and a vacuum state: In a normal state of matter, the particles are constantly bumping into each other.
That keeps everything from becoming too hot or too cold. In a vacuum state, however, the particles don’t interact with each other. So the vacuum state doesn’t experience any friction.
Because there is no friction, the vacuum state can keep expanding forever. In fact, it is possible that the entire universe is currently in a vacuum state.
According to current scientific theories, the universe began in a huge burst of energy known as the Big Bang. Over time, the universe expanded outward.
Now, the universe is 13 billion years old. At this point, the universe has cooled down to just above absolute zero.
The universe is still expanding. However, because there is no friction, its rate of expansion is slowing down. Eventually, the universe will stop expanding altogether. Then, it will begin contracting again.\
When that happens, the universe will once again reach a critical point. At that moment, the universe will explode in another massive burst of energy.
After that, the universe will expand again. And so on and so forth.
But before the universe explodes, it will continue to cool down. Eventually, the temperature will drop below the point where the atoms in the universe can hold their electrons anymore.
At that point, the atoms will collapse into protons and neutrons. Protons and neutrons are two fundamental building blocks of matter. They are also the only things left in the universe after the Big Bang.
So now you know that while it might be difficult to measure vacuum energy, it’s entirely impossible. And for the future of our universe, it’s important too.
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